Method for locating nonlinear mechanical junctions of metallic electrical conductors

ABSTRACT

A technique and apparatus for identifying and accurately locating nonlinear mechanical junctions of electrical conductors whereby RF interference generated by nonlinear junctions can be eliminated. A fundamental signal is applied to a suspected junction by means of a current probe held in close proximity thereto. Receiver apparatus senses whether third harmonic signals are generated thereby. If third harmonic signals are generated the suspected junction is identified as being nonlinear and its exact location is then determined by connecting a bypassing conductor between the suspected location of the nonlinearity and ground and measuring the resultant reduced amplitude third harmonic signals. The exact location is determined when the bypassing conductor is moved as close to the suspected nonlinearity as is physically practical while maintaining the reduced amplitude of the third harmonic signal.

ilnite tates aeat Eisner et al. May E5, 1973 54] METHOD FOR LOCATING3,636,437 1/1972 Soulant et al. .324/34 ST NONLINEAR MECHANICAL3,648,161 3/1972 Soulant 324/34 ST JUNCTIONS OF METALLEC ELECTRKCALCQNDUCTORS Primary Examiner-Gerard R. Strecker Attornev-R. S. Sciasc'a tal. [75] Inventors: Raymond F. Eisner, Lombard; Will e liam F.Lancaster, Oak Lawn, both [57] ABSTRACT of I11.

A technique and apparatus for identifying and accu- [73] Asslgnee The iT rately locating nonlinear mechanical junctions of eleca: ary o etrical conductors whereby RF interference generated as mg by nonlinearjunctions can be eliminated. A funda- [22] Filed: Apr. 13, 1972 mentalsignal is applied to a suspected junction by means of a current probeheld in close proximity [21] Appl' 243728 thereto. Receiver apparatussenses whether third harmonic signals are generated thereby. lf thirdharmonic [52] US. Cl ..324/52 signals are generated the suspectedjunction is [51] Int. Cl. ..G01r 31/08 identified as being nonlinear andits exact location is Fleld Of Search l 52, 54, 66, then determinedonnecting a bypassing onductor 34 ST between the suspected location ofthe nonlinearity and ground and measuring the resultant reduced am- [56]References Clted plitude third harmonic signals. The exact location isUNITED STATES PATENTS determined when the bypassing conductor is movedas close to the suspected nonlinearity as is physically 2,007,772 7/1935Sams et al. ..324/34 practical while maintaining the reduced amplitudeof 3,163,817 12/1964 Simpson ..324/52 the third harmonic ignal 3,299,351l/1967 Williams ..324/52 3 Claims, 1 Drawing Figure SIGNAL SOURCERECEIVER F0 ;20 261 "'0 22 2:3 BANDPASS BANDPASS FILTER FILTER r r 1 B/IO i n n l C I V i D L 1 ease ra a I32 HULL PATEHTEB 3,733 .545

SIGNAL SOURCE REGEIVER F0 ;20 26 0 BANDPASS BA NDPA 5s FILTER FILTERCLAMP AROUND CURRENT PROBE J32 METHOD FOR LOCATING NONLINEAR MECHANICALJUNCTIONS OF METALLIC ELECTRICAL CONDUCTORS CROSS-REFERENCE TO RELATEDAPPLICATIONS The subject matter disclosed herein is closely related toU.S. Pat. No. 3,609,553 by Marvin J. Fraser et al. assigned to theUnited States of America as represented by the Secretary of the Navy andto U.S. Pat. application Ser. No. 239,066 entitled ApparatusforDetecting Natural Nonlinearities in Antennas," filed on 3-2- 9-72, byR. F. Elsner et al. and assigned to thesame assignee as above.

BACKGROUND OF THE INVENTION As disclosed in the above-referenced patentapplication and patent, the United State Navy is very concerned withidentifying, classifying and locating RF interference sources aboardnaval ships due to the detrimental effects which RF interference canhave on the normal operation of communication systems. One such sourcecomprises nonlinear junctions of metallic conductors such as pipes,ladders, etc. found on most ships. Various prior art schemes have beenused to approximate the general location of interference-producingnonlinearities. These schemes, however, cannot be used to locate theactual nonlinearity itself whereby corrective action can be taken. Forexample, spurious signals generated by a nonlinearity can be traced to anetwork of under-deck piping, but the nonlinearity itself can often notbe pinpointed. As a result this source of radio frequency interferencecannot be eliminated. In addition to pinpointing nonlinearities, thedevice to be disclosed herein can further be used by shipyard personnelto evaluate the electrical performance of bonding straps applied acrossknown or suspected nonlinearities such as mechanically loose fittingsand which are often interference generators themselves.

SUMMARY OF THE INVENTION A technique for eliminating RF interferencegenerators by identifying and locating nonlinear mechanical junctions ofmetallic, electrical conductors located in the general vicinity ofcommunication systems. Suspected junctions are fed fundamental signalswhereby they will generate third harmonic signals if they are nonlinear.Once it is determined that they are nonlinear, a bypass conductor isconnected between the suspected exact location of each junction andground and the amplitude of the third harmonic signals generated iscompared to the amplitude generated in an unbypassed condition. Asubstantially zero or reduced amplitude in the bypassed conditionindicates the direction in which the nonlinearity lies. The exactlocation is determined when the bypassing conductor is moved as close tothe suspected nonlinearity as is physically practical while maintainingthe reduced amplitude of the third harmonic signal.

STATEMENT OF THE OBJECTS OF THE INVENTION It is the primary object ofthe present invention to describe a relatively simple technique andapparatus for locating precisely an RF interference-producing, nonlinearjunction existing somewhere along a metallic conductor.

Other objects, advantages and novel features of the invention willbecome apparent from the following detailed description of the inventionwhen considered in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWING The drawing is a simplified blockdiagram of electrical apparatus embodying the inventive conceptdisclosed herein and shown in conjunction with a metallic lifeline-ofthe type normally found on naval ships and which can comprise a sourceof RF interference if it has nonlinear mechanical junctions, i.e.,metal-tometal junctions.

DESCRIPTION OF THE PREFERRED EMBODIMENT In the drawing, the apparatusembodying the present inventive concept is shown being used to locatenonlinear mechanical junctions which exist somewhere along themechanical junctions which exist along the lifeline 10. The lifeline isof the conventional type found on naval ships and terminates in aturnbuckle assembly 12 which is hooked to a welded loop 14 on a metalstanchion 16 thereby providing a metal-to-metal contact or junction. Thestanchions 16 are normally welded to the hull 18 of a naval ship (notshown).

The electrical apparatus basically comprises a signal source 20 operableat a selectable fundamental frequency F The output of the signal sourceis filtered by the bandpass filter 22 which is centered at the frequencyF The filtered output is coupled to a conventional clamp-around currentprobe 24. The probe is shown clamped around the metal conductor 10.

The output of the probe 24 is fed to the receiver 26 which is centeredto receive third-harmonic currents generated by the signal source 20 innonlinear junctions of the lifeline 10. A bandpass receive filter 28 iscentered at the third-harmonic and assures that only this signal isreceived at the receiver.

For simplicity a shipboard metallic lifeline 10 has been selected toillustrate and describe the operation of the apparatus. As statedearlier, each end of the metallic lifeline normally terminates in aturnbuckle assembly 12 which is hooked to a welded loop 14 on a metalstanchion 16. If one or both of these turnbuckle stanchion interfaces orjunctions A and B are nonlinear, then interference could be generated bysignals induced in the lifeline by strong emanations from transmittingantennas on the ship. These nonlinearity generated radio frequencysignals could then be received by the ships receiving system asundesired interference.

In operation, the directional nonlinearity locator provides a filteredsignal at frequency F to the clamparound current probe 24. If either ofthe terminations A or B or both comprise nonlinear junctions, athirdharmonic signal will be generated and fed to the receiver 26through the filter 28. Should both junctions be linear, nothird-harmonic signal will be generated. Thus once it has beendetermined that either junction or both are nonlinear each junction canbe tested individually to determine its exact location by simplebypassing technique as follows.

Assuming that the junction A is nonlinear and that the junction B islinear, then temporarily connecting points C and C with a metallicconductor 30 will reduce the fundamental current F fed to the junction Aand will also reduce the magnitude of any thirdharmonic signal 3Fgenerated by junction A. Conversely, if the conductor joining points Cand C is removed and reconnected across points D and D, then the strongfundamental F will be fed to the nonlinear junction A and a strongthird-harmonic signal 3P will be detected by the receiver.

In essence therefore, a zero or reduced thirdharmonic amplitude isobtained when the nonlinear junction is bypassed. By noting or measuringthe thirdharmonic amplitudes, as each junction is bypassed in turn, thedirection in which the nonlinear junction lies can thus be readilydetermined. As a further step, the current probe can be moved closer tothe nonlinear junction in the direction indicated and the bypassingprocedure repeated until the nonlinear junction is pinpointed precisely.

If both junctions are linear no third-harmonic current will be obtainedat the receiver. If both are nonlinear, strong third-harmonic outputswill be obtained from both bypassing conditions. Individual nonlinearjunctions can be evaluated by placing the current probe around eachstanchion in turn, and then applying the bypassing conductor as above.Should either junction be linear, resistive, open, or shorted, thedevice can be made to perform its function by choosing F so that areasonable F current is induced into the line even if the line were tobe open-circuited at both ends (that is, even if the line approximated adipole antenna).

It should be understood that although the drawing illustrates a lifelineas metallic conductor, the apparatus and technique can be advantageouslyutilized on other items such as ladders, pipes, cable armors, etc.,where multiple nonlinear mechanical junctions may be present.Furthermore, it can be appreciated that the device is especiallyadvantageous for the following reasons. First, it can test suspecteditems for nonlinearity in a simple, yet highly effective manner, and canbe used to pinpoint the exact location of nonlinearities in complexenvironments such as communications systems aboard naval ships. Aftersuch nonlinearities have been eliminated, the technique can be used toverify this fact. Furthermore, suspected nonlinear items may be testedfor nonlinearity without using the transmitting or receiving equipmentof the communication system aboard the ship. Finally, the deviceobviously can be made very small and self-contained which is a veryimportant consideration on naval ships where space is very limited.

Obviously many modifications and variations of the present invention arepossible in the light of the above teachings. It is therefore to beunderstood that within the scope of the appended claims the inventionmay be practiced otherwise than as specifically described.

What is claimed is:

1. A techniquefor accurately locating nonlinear mechanical junctions ofmetallic conductors to eliminate RF interference comprising the stepsof:

applying a fundamental signal to a suspected junction by means of acurrent probe held in close proximity thereto; sensing anythird-harmonic currents generated thereby if said suspected junction isnonlinear;

bypassing a portion of said fundamental signal from said suspectedjunction by connecting a metallic bypass conductor between the generallocation of said junction and ground;

sensing the magnitude of third-harmonic currents generated thereby;

comparing said magnitude relative to the magnitude of saidthird-harmonic currents generated in an unbypassed condition;

connecting said bypass conductor at various points of said suspectedjunction and in a direction relative to the first such connectionindicated by decreasing third-harmonic magnitudes,

whereby the exact location of said junction is determined when saidbypass conductor is connected as close as possible to said nonlinearjunction whereby a substantially constant reduced magnitude is obtained.

2. Apparatus for accurately locating nonlinear mechanical junctions ofmetallic conductors comprising:

signal source means for providing a fundamental signal at a frequency Ffirst bandpass filter means centered at F connected across the output ofsaid signal source means;

current probe means connected at the input thereof to the output of saidfirst bandpass filter for applying said fundamental signal to suspectedmechanical junctions of said metallic conductors; second bandpass filtermeans centered at the thirdharmonic, 3F of said fundamental signalsconnected to the output of said current probe means;

receiver means connected to the output of said second bandpass filtermeans for sensing thirdharmonic currents generated by said suspectedmechanical junctions; and,

conductor means for bypassing portions of said fundamental signal fromsaid suspected junctions whereby the exact location of nonlinearmechanical junctions is obtained when the magnitude of saidthird-harmonic currents is reduced or is substantially equal to zerowhen said bypassing conductor is positioned as close to the suspectednonlinear junction as is physically possible.

3. The apparatus of claim 2 wherein said current probe comprises aclamp-around device.

1. A technique for accurately locating nonlinear mechanical junctions ofmetallic conductors to eliminate RF interference comprising the stepsof: applying a fundamental signal to a suspected junction by means of acurrent probe held in close proximity thereto; sensing anythird-harmonic currents generated thereby if said suspected junction isnonlinear; bypassing a portion of said fundamental signal from saidsuspected junction by connecting a metallic bypass conductor between thegeneral location of said junction and ground; sensing the magnitude ofthird-harmonic currents generated thereby; comparing said magnituderelative to the magnitude of said third-harmonic currents generated inan un-bypassed condition; connecting said bypass conductor at variouspoints of said suspected junction and in a direction relative to thefirst such connection indicated by decreasing third-harmonic magnitudes,whereby the exact location of said junction is determined when saidbypass conductor is connected as close as possible to said nonlinearjunction whereby a substantially constant reduced magnitude is obtained.2. APparatus for accurately locating nonlinear mechanical junctions ofmetallic conductors comprising: signal source means for providing afundamental signal at a frequency Fo; first bandpass filter meanscentered at Fo connected across the output of said signal source means;current probe means connected at the input thereof to the output of saidfirst bandpass filter for applying said fundamental signal to suspectedmechanical junctions of said metallic conductors; second bandpass filtermeans centered at the third-harmonic, 3Fo of said fundamental signalsconnected to the output of said current probe means; receiver meansconnected to the output of said second bandpass filter means for sensingthird-harmonic currents generated by said suspected mechanicaljunctions; and, conductor means for bypassing portions of saidfundamental signal from said suspected junctions whereby the exactlocation of nonlinear mechanical junctions is obtained when themagnitude of said third-harmonic currents is reduced or is substantiallyequal to zero when said bypassing conductor is positioned as close tothe suspected nonlinear junction as is physically possible.
 3. Theapparatus of claim 2 wherein said current probe comprises a clamp-arounddevice.